Nitrogen Metabolism

Ammonia produced by nitrogen fixation or nitrate assimilation cannot be allowed to accumulate freely, since it is toxic to cells, so plants convert it into amino acids through two routes, together called ammonium assimilation. In reductive amination, ammonia reacts directly with alpha-ketoglutaric acid to form the amino acid glutamic acid (glutamate). In catalytic amination, also known as the GS/GOGAT pathway, the enzyme glutamine synthetase (GS) first combines glutamate with ammonium (NH4+), using ATP, to form the amide glutamine; the enzyme GOGAT (glutamine-2-oxoglutarate aminotransferase) then reacts this glutamine with a further molecule of alpha-ketoglutaric acid, using NADH, to yield two molecules of glutamate - one of which re-enters the cycle …